Manganese alloys



Patented July 27, 1943 2,325,044 MANGANESE ALLOYS Reginald S. Dean, Salt Lake City, Utah, assignor to Chicago Development Company, Chicago, Ill.,.a corporation of Illinois a No Drawing. Application July 12, 1941, Serial No. 402,238

Claims.

My invention relates to the preparation and heat treatment of alloys consisting essentially of manganese, iron and chromium, and is particullarly concerned with the preparation of such alloys which are highly resistant to atmospheric corrosion, possess the ability to withstand great extension by cold work without the hardening which is characteristic of austenitic stainless steels and irons heretofore known in the art, and, in addition, have the properties of retaining work-hardening at relatively high temperatures, of hardening and being rendered non-magnetic, without embrittlement, by heat treatment.

Alloys of manganese, chromium and iron have heretofore been suggested but, in all cases, those alloys whose properties have been investigated have contained a substantial content of carbon, of the order of 1% or more, although suggestions have been made for alloys where the carbon content was allegedly zero. In such alloys of the prior art, themanganese content always was less than that of the chromium. Such alloys are disclosed by the prior art to have a magnetic permeability not exceeding from 2 to 5% of that of cast iron. In other known alloys containing manganese, chromium and iron, both carbon and silicon are present, the silicon comprising in excess of 3% andupto8%.

The alloys of my invention are sharply distingulshable from those of the prior art not only in composition but in physical characteristics and properties, including amenability to difierent types of heat treatment. ThusQfor example, the alloys of my invention must be substantially free from the oxides of silicon and aluminum, carbon is substantially, and preferably entirely, absent, and silicon should not exceed 1% and is preferably present in amounts less than 0.7% and particularly close to 0%. In connection with the matter of properties of the alloys of my inven--- tion, it may be pointed out, among other things, that their magnetic permeability, after quenching from high temperatures, is substantially that of cast iron, a property which distinguishes radiaclilly from numerous of the alloys of the prior Again, there is a definite and radical diflerence between the heat treatment proposed by the prior art as applied to alloys of manganese, chromium and iron and the heat treatments which I utilize.

The heat treatment of the alloys of the present invention usually consists of a quenching, cold working and reheating procedure, the quenching taking place from a temperature higher than 1100 degrees C. and particularly about 1200 degrees C.

The heat treatment described in the prior art with respect to manganese, iron, chromium alloys involves heating the cast alloy to 1000 degrees C. to 1100 degrees C. for several hours and then cooling in the furnace. Such a' heat treatment does not produce increased strength in the alloys of my invention. Here it has no substantial effect on the hardness or produces a softening, depending upon the rate at which the alloys were cooled in casting. Heating the alloys of my present invention to 1000 degrees C. causes softening without the reappearance of magnetism, that is; they are not carried into the state from which they were quenched. This state is only attained at higher temperatures, usually above 1100 degrees C.

It will be seen, therefore, as hereinafter pointed out in detail, that, by a suitable selection of alloy composition and by heating of the alloys to approximately 1200 degrees C. and quenching, I may cold work the said alloys by rolling, swaging or by any other means to an extent of 90% or more reduction in area without excessive hardening. By excessive hardening, I refer to any hardness above about 25 as measured on the Rockwell C scale. I have found that the range of'alloy composition in which this phase of my invention may be practiced may be defined approximately as follows: From 10% to 30% manganese, the chromium content should, range from about 17.5% to approximately 30%. As the manganese content increases above 30%, the range of chromium content is lowered. Thus, for example, at 40% manganese, the chromium content should be between about 12.5% and about 16%. The manganese should, in all cases, be at least 10% for the practice of my present invention.

The following table illustrates representative alloys falling within the scope of my invention.

All of the said alloys are heated to 1200 degrees C. and quenched in water before cold working.

Rloclawell 0 Per cent Per cent Per cent 31' ness cold worked Mn or F6 reductio'n 11] area 30 1s 52 2'; 20 1s 62 22 20 20 so 21 20 22 5s 24 20 24 56 24 2o 2s 54 23 20 2s 52 22 20 30 50 24 All of the alloys in the range' of compositionset out hereinabove, as previously indicated, have a magnetic permeability of th same order as that of cast iron.

The alloys within the composition range which I have set forth hereinabove, as previously stated, may be greatly hardened and strengthened by heat treatment after quenching from about 1200 degrees C. and cold working. I have found, for example, .that all -of the above described alloys may be hardened by heating to temperatures between about 400 degrees C. and about 800 degrees C. after quenching from approximately 1200 degrees C. and cold working. I have found, however, that when the chromium exceeds a 'certain percentage within the above described range,

the alloys may be embrittled by reheating within the range of 400 degrees C. to 800 degrees C. while, if the chromium is maintained below the limiting percent, hardening without embrittlement may be obtained. This upper percentage of chromium whereby hardening without embrittlement is obtained varies from 30% chromium, where the manganese content is 10%, to 12% chromium where the manganese content is 40%. This range or variation in the limiting percentage of chromium is substantially linear. While the amount of hardening which is obtainable in the alloys of my invention varies somewhat with the temperature of heat treatment, the important factor is, however, that, by the practice of my invention, hardening may be obtained without embrittlement. For the purpose of illustrating this phase of my invention, the following examples are set forth hereinbelow:

Hard- Per cent Per cent ness gig' g Mn Cr cold 3 worked g 18 23 i 48 25 20 t 20 2i 53 32 a0 18 I 23 51 28 While there is a small amount of hardening below the critical percentage of chromium, the range of hardening is, however, materially less than above the critical percentage of chromium for best coldworking, and, accordingly, I prefer particularly to utilize those alloys having more than the critical amount of chromium in the practice of the preferred aspects of my invention. In certain cases, some useful results may be obtained with not more than 2.5% less than the critical amount of chromium as hereinabove It should be understood that the hardness of the alloys, after reheating to about 600 degrees C., is not necessarily the maximum hardness which can be obtained. Hardening at this temperature is described for the purpose of illustrating. the fact that the alloys of my present invention do not become brittle on heat treatment, since I have found that, if alloys of manganese, chromium and ironv become brittle by reheating at any temperature, they do soat about 600 degrees C. It is not uncommon, for example, to obtain hardnesses' as high as about Rockwell C 60 by heating at temperatures somewhat below 600 degrees C. The lower limit of manganese in the alloys with which the present invention deals and which will harden by heat treatment after cold work in accordance with the teachings of my present invention to produce useful alloys is about 16% manganese, although I prefer that the manganese be present in amounts of at least 20% in order to obtain the. best results.

I have also found that certain of the alloys of the present invention, in addition to hardening effectively by quenching and reheating, may be hardened without'embrittlement by heating to about 1200 degrees C. and slow cooling. Those of the alloys of the present invention which have this property fall within the composition limits of about 22 to about 28% manganese, about 15 to about 30% chromium, balance iron.

It should be understood that I consider an alloy brittle when it will not give a reading on the Rockwell C scale without chipping. I have found this to be a reliable indication of the extent of brittleness which renders an alloy useless or substantially so for at least most commercial purposes.

In the practice of my invention, I prefer to employ electrolytic iron, electrolytic chromium and electrolytic manganese of high purity so as not to introduce deleterious constituents into the alloys. I have found, for example, that the presence of oxides of aluminum and silicon, such as are present in silico-tliermic or alumino-thermic manganese or ferro-ma'nganese prevents the effective practice of my invention. While the manganese which I employ may be produced by a vacuum distillation process, I prefer, particularly, to employ electrolytic manganese having a purgty of at least about 99.0% and preferably of 99. I

By virtue of their hardening by reheating after quenching, particularly with intermediate cold work, my'alloys are particularly useful for- .various purposes as, for example, gears, bearings,

amour plate, and forpurposes, in general, where case-hardened nickel or nickel-chromium steels have heretofore been used. The alloys of my present invention, hardened as described herein, have a wide utility in articles of cutlery, ball and roller bearings, toolsv and dies, especially saws, and other tools which are necessarily exposed to corrosive influences. In the soft state,

- the alloys of my present invention maybe employed for cooking utensils and other purposes .where a relatively soft material of satisfactory 501, filed July 16, 1938 and Serial No. 267,706,

filed April 13, 1939.

" iron, chromium and manganese in the form of What I claim as new and desire to protect by Letters Patent of the United States is:

hit process of producing stainless alloys of greatly cold worked rods, sheet or wire which :comprises selecting an alloy within the composi- 3. A process of producing hardened stainless 1 alloys of iron, chromium and manganese in the form of greatly cold worked rods, sheet or wire which comprises selecting an alloy within the composition range 20 to 30 per centmanganese, 16 to 20 per cent chromium, balance substantially all iron, heating said alloy to approximately 1200 degrees 0., quenching, and cold working. I v

4. A process of'producing hardened stainless alloys of iron, chromium and manganese in the form of greatly 'cold worked rods, sheet or wire.

which comprises selecting an alloy within the compositionrange 20'to 30 per cent high purity electrolytic manganese, 16 to 20 per cent high purity electrolytic chromium, balance substan-' tially all high purity electrolytic iron, heating said alloy to approximately 1200 degrees 0., quenching, coldworking, and reheating between 400 and 800 degrees 0. p a

.5. A process of producing hardened iron, chromium and manganese alloys in a form obtained' by a relatively large amount of cold work which comprises selecting an alloy of iron, manganese and chromium within the composition range 10 to 40 per cent manganese, 16 to 30 per cent chromium, balance substantially all iron,

quenching said alloy from about 1200 degrees 0.,

cold working 'said alloy, and then hardening the same-by heating to. temperatures between 400.

degrees and 800 degrees 0.

6. A process of producing iron, chromium and manganese alloys. in a hardened state having a form obtained by relatively large reduction by cold work, which comprises selecting an alloy within the'composltion range 16 to -30 per cent manganese, 17.5 to 30 per cent chromium, balance substantially all iron, heating said alloy to approximately 1200 degrees 0., quenching, cold working said alloy tothe desired dimensions, and Y reheating said alloy to a temperature between 400 degrees C. and 800 degrees 0. "I. A process of producing iron, chromium and manganese alloys in a hardened but not brittle state and in a form obtained by a relatively large amount or cold worn-which comprises selecting .an alloyot iron, manganese and chromium within the composition range 10 to 40 per cent manganese, 12 to 30 per cent chromium,

' balance substantially all iron, the percentage 01' chromium being less than '30 per cent when the manganese content is 10 per cent, and less than 12 per cent when the manganese content. is 40 v percent, intermediate percentages of chromium being in general linear relation-to intermediate percentages of manganese, quenching said alloy from 1200 degrees 0., forming the same by a cold working process, and hardening by heating to temperatures between 400 degrees and 800 degrees C.

8. Stainless alloys consisting essentially of manganese, chromium and iron, said alloys being in hardened torm, resulting from quenching from approximately 1200 degrees 0., cold work-, ing, and reheating within the, range of about 400 degrees-,0. to 800 degrees 0., the alloy -constituents being present in substantially the followlng proportions: 10 to- 40% 01' high purity electrolytic manganese, 16 to- 30% high purity electrolytic chromium, and balance high purity iron.

9. Stainless alloys consisting essentially of manganese, chromium and iron, said alloys being in hardened form-resulting from quenching from approximately 1200 degrees 0., cold working. and reheating within the range or about 400 degrees 0. to 800 degrees 0., the alloy constituents being present in substantially the following proportions: 16 to 30 per centv high purity.

manganese, 16 to 30 per cent chromium, and .bal-

10. Stainless alloys consisting essentially o manganese, chromium and iron, said alloys being in hardened form, resulting from quenching from approximately 1200 degrees 0., cold work-- -'ing, and reheating within the range of about 400 degrees 0. to 800 degrees 0., the alloy con-,

ammam a. nun. 

